Folmer Dineke E, van der Mark Vincent A, Ho-Mok Kam S, Oude Elferink Ronald P J, Paulusma Coen C
AMC Liver Center, Academic Medical Center, Amsterdam, The Netherlands.
Hepatology. 2009 Nov;50(5):1597-605. doi: 10.1002/hep.23158.
Mutations in ATP8B1 cause progressive familial intrahepatic cholestasis type 1 (PFIC1) and benign recurrent intrahepatic cholestasis type 1 (BRIC1), forming a spectrum of cholestatic disease. Whereas PFIC1 is a progressive, endstage liver disease, BRIC1 patients suffer from episodic periods of cholestasis that resolve spontaneously. At present it is not clear how the type and location of the mutations relate to the clinical manifestations of PFIC1 and BRIC1. ATP8B1 localizes to the canalicular membrane of hepatocytes where it mediates the inward translocation of phosphatidylserine. ATP8B1 interacts with CDC50A, which is required for endoplasmic reticulum exit and plasma membrane localization. In this study we analyzed a panel of missense mutations causing PFIC1 (G308V, D554N, G1040R) or BRIC1 (D70N, I661T). In addition, we included two mutations that have been associated with intrahepatic cholestasis of pregnancy (ICP) (D70N, R867C). We examined the effect of these mutations on protein stability and interaction with CDC50A in Chinese hamster ovary cells, and studied the subcellular localization in WIF-B9 cells. Protein stability was reduced for three out of six mutations studied. Two out of three PFIC1 mutant proteins did not interact with CDC50A, whereas BRIC1/ICP mutants displayed reduced interaction. Importantly, none of the PFIC1 mutants were detectable in the canalicular membrane of WIF-B9 cells, whereas all BRIC1/ICP mutants displayed the same cellular staining pattern as wild-type ATP8B1. Our data indicate that PFIC1 mutations lead to the complete absence of canalicular expression, whereas in BRIC1/ICP residual protein is expressed in the canalicular membrane.
These data provide an explanation for the difference in severity between the phenotypes of PFIC1 and BRIC1.
ATP8B1基因的突变会导致1型进行性家族性肝内胆汁淤积症（PFIC1）和1型良性复发性肝内胆汁淤积症（BRIC1），形成一系列胆汁淤积性疾病。PFIC1是一种进行性终末期肝病，而BRIC1患者会经历胆汁淤积的发作期，这些发作期会自发缓解。目前尚不清楚突变的类型和位置如何与PFIC1和BRIC1的临床表现相关。ATP8B1定位于肝细胞的胆小管膜，在那里它介导磷脂酰丝氨酸的向内转运。ATP8B1与CDC50A相互作用，CDC50A是内质网出口和质膜定位所必需的。在本研究中，我们分析了一组导致PFIC1（G308V、D554N、G1040R）或BRIC1（D70N、I661T）的错义突变。此外，我们还纳入了两个与妊娠期肝内胆汁淤积症（ICP）相关的突变（D70N、R867C）。我们研究了这些突变对中国仓鼠卵巢细胞中蛋白质稳定性以及与CDC50A相互作用的影响，并在WIF-B9细胞中研究了亚细胞定位。在所研究的六个突变中有三个导致蛋白质稳定性降低。三个PFIC1突变蛋白中有两个不与CDC50A相互作用，而BRIC1/ICP突变体显示出相互作用减弱。重要的是，在WIF-B9细胞的胆小管膜中未检测到任何PFIC1突变体，而所有BRIC1/ICP突变体与野生型ATP8B1显示相同的细胞染色模式。我们的数据表明，PFIC1突变导致胆小管表达完全缺失，而在BRIC1/ICP中，残余蛋白在胆小管膜中表达。
这些数据为PFIC1和BRIC1表型严重程度的差异提供了解释。
